Chronic diseases generally require administering of medicaments or drugs according to a pre-defined time schedule in order to keep the concentration level of a pharmaceutically active substance on a pre-defined level. Many medicaments require administration by way of injection by making use of syringes or syringe-like drug delivery devices. Such devices should be universally applicable and should be operable even by persons without formal medical training.
Moreover, such devices, like pen-type injectors should provide accurate, precise and reliable setting of a dose and subsequent dispensing of the respective medicament. Typically, the medicament to be dispensed and injected is provided in a disposable or replaceable cartridge, such as a vial, an ampoule or a carpule comprising a slidably disposed piston to become operably engaged with a piston rod of a drive mechanism of the drug delivery device. The drive mechanism is adapted to apply thrust to the cartridge's piston in distal direction in order to build-up a respective fluid pressure, which in turn leads to a dispensing of the liquid medicament via a dispensing or distal end of the cartridge being typically in fluid connection with a piercing element like an injection needle.
It is generally of importance, that the patient strictly follows a given prescription schedule. However, patients that already got used to the medicament for a long time or patients that suffer side effects of a chronic disease and which may be physically or even cognitively impaired, compliance of the prescription schedule is sometimes sub-optimal. Since a large variety of existing drug delivery devices is implemented all-mechanically, it is further rather difficult for an attending physician to control, whether the patient strictly follows a given prescription schedule.
Document WO 2010/098927 A1 describes a medical module for a drug delivery pen configured to be attached to a disposable drug delivery pen so that the module may determine: selected dosage, injection of selected dosage, duration of injection, time of injection and other injection-related parameters. The medical module comprises a dosage sensor coupled to a primary module housing and a follower portion connected to the dosage sensor and disposed for movement relative to the primary module housing. Furthermore, retention forks are provided that are connected to the follower portion. Said retention forks are configured to capture an actuation button of a drug delivery pen there between.
The dosage sensor is preferably a linear potentiometer and is used to measure the position of a dosage selector of the drug delivery pen for determining the size of a bolus injected by a user. When the drug delivery device comprises a rotatable and axially displaceable dose setting component, like a dosage selector being operable in a screw-like manner, it is suggested to frictionally couple the dosage selector of the pen with a capture ring which in turn is coupled to a follower. The capture ring may further be provided with external splines or teeth that are in engagement with internal splines or teeth of a rotatable knob. This knob is provided with a through opening to allow actuation button of the pen to protrude through the opening for engagement by the user.
Hence, the medical module comprises numerous mechanically interacting components to mechanically couple the medical module with a dosage selector of the pen injector. The module therefore comprises a comparatively large number of mutually interacting mechanical components, which may become prone to failure.